Isomerization solvents

ABSTRACT

Benzene, which contains at least four substituted halogens, is an effective solvent for a Lewis acid catalyst employed in the isomerization of hydrocarbons. A particularly preferred isomerization solvent is 1,2,3,4-tetrachlorobenzene and is used in conjunction with aluminum bromide. In another aspect of this invention, if hydrogen, with or without added hydrogenation components, is added to the catalyst system, the isomerization selectivity of the reaction is greatly improved and the life of the catalyst system itself is greatly enhanced. When substantial amounts of benzene are present in the feed, a hydrogenation component is added to the system so that the benzene is hydrogenated to cyclohexane which is then subsequently isomerized to methylcyclopentane.

ijnited States Patent 1 Kramer [45} Sept. 11,1973

[ ISOMERIZATION SOLVENTS George M. Kramer, Berkeley Heights, NJ.

[73] Assignee: Esso Research and Engineering Company, Linden, NJ.

[22] Filed: June 2, 1971 [21] Appl. No.: 149,368

Related US. Application Data [63] Continuation-in-part of Ser. No.28,039, April I3,

1970, abandoned.

[75] Inventor:

[52] U.S. Cl 260/668 A, 260/68365 260/6837 Primary ExaminerCurtis R.Davis Attorney-Chasan & Sinnock and John Paul Corcoran [57] ABSTRACTBenzene, which contains at least four substituted halogens, is aneffective solvent for a Lewis acid catalyst employed in theisomerization of hydrocarbons. A particularly preferred isomerizationsolvent is l,2,3,4-tetrachlorobenzene and is used in conjunction withaluminum bromide. In another aspect of this invention, if hydrogen, withor without added hydrogenation components, is added to the catalystsystem, the isomerization selectivity of the reaction is greatlyimproved and the life of the catalyst system itself is greatly enhanced.When substantial amounts of benzene are present in the feed, ahydrogenation component is added to the system so that the benzene ishydrogenated to cyclohexane which is then subsequently isomerized tomethylcyclopentane.

19 Claims, No Drawings rsomsmznrou SOLVENTS This application is acontinuation-in-part of an application and bearing Ser. No. 28,039,which was filed on Apr. 13, 1970, and now abandoned.

The isomerization of aliphaticand aromatic hydrocarbons is well known.Specifically, C to C paraffins have been isomerized in the past toproduce highly branched isomers for use as high octane blendingcomponents for motor fuels.

Typically, n-pentane has been known to be isomerized to isopentane, andnormal hexane or normal heptane have been known to be isomerized toequilibrium mixtures of the most highly branched components like2,2-dimethylbutane, 2,3-dimethylbutane and 2,2,3- trimethylbutane.Normal butane is often isomerized to isobutane and the latter issubsequently used in commercial alkylation reactions with olefins toform high octane blending components for motor fuels.

Heretofore, ithas been known to make use of various solvents in theisomerization of aliphatic and aromatic materials. In particular, normaland isoparaffins have been employed with Lewis Acid catalysts asdisclosed in US. Pat. No. 2,987,563.

The use of a solution of aluminum bromide permits a more efficient useof the catalyst than when the aluminum bromide is adsorbed onto a solidsupport. In solution, aluminum bromide is highly dispersed but on asolid support it is held closely to the surface and only the uppermostor outermost layer of the aluminum'bromide can be considered to beeffective at any one time. This means that the solid supported catalystis subject to inhibition or poisoning by subsequentadsorption of asurface coating of asludge or some form of inhibitor which need only bepresent in low concentration, i.e., just enough to cover the surface, inorder to deactivate the catalyst The liquid catalyst system of thesubject invention, because of its high degree of dispersion, isinherently more resistant to inhibitors or poisons'which is an importantadvantage of these systems over the supported catalyst systems. Anotheradvantage of the liquid systems is that they provide more reproducibleand com trollable catalysts than do those systems using a catalystsupport.

The supports generally are not well defined systems that contain at thesurface impurities, which if present Y in the bulk in the long runaffect catalyst performance and activity.

In thepast,the hydrocarbons themselves-have been used as solvents;however, these suffer the, disadvantage of not being'able to remain as ahomogeneous liqit is subject to inhibition by adsorptionof -a surfacecoating of relatively inert compounds such as with a solid support andmay be deactivated by other unknown paths. v

Other solvents such as chlorobenzene and nitrobenzene or nitroalkaneshave also been used to prepare homogeneous solutions of aluminum halidesand paraffins for isomerization purposes. However, these solvents havegenerally been found to interact too strongly with the aluminum halideto allow it to be of much use asa paraffin isomerization catalyst. Thesesystems are useful for accomplishing reactions that only requiremoderately strong acids (i.e., the alkylation of aromatics witholefins), but the solvents are generally too basic to permit theisomerization of paraffins.

US. Pat.' No. 2,987,563 discloses as solvents the l,2,3-trichlorobenzeneor the 1,2,4-trichlorobenzene systems that have been of most value asmedia for paraffin isomerization. Although this solvent represents asignificant improvement over the art, it was limited somewhat in itsrate of activity.

it has been found that the difficulties experienced with paraffins andthe other solvents just described can be substantially overcome by usingthe process at the instant invention. For example, by usingl,2,3,4-tetrachlorobenzene as a solvent for aluminum bromide, a solutionis obtained which mixes readily with hexane and which can easily bepromoted so as to cause a more rapid, selective and efficientisomerization than previously possible. When solutions are promoted withHBr and/or H,O, one can either conduct a purely homogeneousisomerization or obtain a partially miscible twophase liquid system,(hexane in one phase and AlBr l,2,3,4-tetrachlorobenzene in the other).The homogeneous system is obtained at lower l-lBr pressures andcorresponds to less activity than the mixed phase system. t

The two-phase system is formed at higher HBr pressures and is markedlydifferent than the two-phase sys- I reactions and prevent the in situformation of inhibitions as well as to remove contaminants that may bein the feed. r r v For example, an article relating to the isomerizationvof'p 'entanes and hexanes and authoredby B. L. Evering, E..D."DOuville, A. TQLien and R. C Wall was published in the Industrialand-Engineering Chemistry,

Vol. 45 in March of 1953' and discloses that in theuse of aluminumchloride the introduction of hydrogen is effective for pentaneisomerization.-When isomerizing pentane, this article; states thathydrogen pressures must be between l30and 200 pounds per square inch andthe temperature must be as high as l 50C. At temperatures as high asl50C. a partial hydrogen pressure of 900 pounds persquare inch isnecessary in order to prevent the occurrence of side chain reactions.Furthermore,'in the isomerization of hexane using the aluminum chloridesystem, it is seen that at C. a hydrogen pressureof 1,000 pounds persquare inch is required -to be. effective in inhibiting side reactions,whereas'if the hydrogen pressure was lowered to 500 pounds per squareinch and the reaction temperature was increased to l50C. there was agross amount of butane and lighter ends formed in the isomerizationreaction.

it has also been found that if hydrogen is added during'theisomerization of the hydrocarbons using the catalyst system of thesubject invention, that the selectivity and life of the catalyst systemis greatly improved. This permits a highly selective isomerization ofhexane to 2,2-dimethylbutane. For example, the presence of hydrogen inthe catalyst system of the subject invention permits a highly selectiveisomerization of hexane to 2,2-dimethylbutane (i.e., towards equilibriumC distribution) in a continuous manner.

In the subject catalyst system it has been discovered that the hydrogenpressure can be as low as 10 pounds per square gauge inch and does nothave to exceed over 200 pounds per square inch in order to eliminate theside reactions.

Briefly, this invention comprises a process for isomerizing hydrocarbonswhich comprises a step of contacting said hydrocarbons underisomerization conditions in the liquid phase with a Lewis acid catalyst,said Lewis acid catalyst being dissolved in a tetra-halosubstitutedbenzene.

In another embodiment, this invention comprises a step of addinghydrogen at pressures ranging from 10 to 200 psig.

In yet another embodiment this invention comprises carrying out thereaction in the presence of a hydrogenation catalyst. The hydrocarbonsis isomerized by the process of the subject invention can be normalparaffins having a chain length of C or higher, preferred normalparaffins to be isomerized are those having a chain length ranging fromC to C Typical isomerization reactions which would take place accordingto the process of the instant invention include the conversion of normalpentane to isopentane, normal butane to isobutane, n-hexane toisohexane, n-heptane and C naphthas to highly branched isomers such as2,2,3-

trimethylbutane, 2,2-dimethylpentane, 3 ,3- dimethylpentane,2,3-dimethylpentane and 2,4- dimethylpentane.

The instant process may also be utilized to isomerize methylcylopentaneto cyclohexane which is valuable as a chemical intermediate and to thegeneral isomerization of alkyl cycloalkanes to the equilibriumdistribution of isomers.

Aromatic compounds containing methyl and ethyl side chains undergoisomerization by the subject catalyst system. For example, any of thexylenes may be isomerized to an equilibrium mixture of its three isomersand this is useful because of the difference in value of the isomers asintermediates for further chemical processing. Aromatic compounds alsoundergo disproportionation reactions with the catalyst system. Forexample, isopropyl benzene readily yields benzene and diisopropylbenzenewhile toluene slowly reacts to form benzene and xylenes.

Typical feedstreams would include normal paraffins found within anaphtha boiling between 10F. and 210F. Additionally, the butane streamobtained at the tail end of the butane-olefin alkylation process as wellas the paraffins remaining after extracting light olefins from catcracked streams and the light components coming from the powerformingreaction are good sources .of feed. With relation to the aromaticswhichmay be isomerized by the instant process, xylenes, trimethylbenzenes,and tetramethylbenzenes are suitable feeds that can be obtained fromvirgin naphthas, catalytic reformers or catalytic crackers.

The catalyst for this isomerization reaction is a Lewis acid. As definedin this invention, a Lewis acid is any molecule, radical or ion in whichthe normal electron grouping about a given atom is incomplete so thatthe atom may accept an electron pair or pairs. The preferred Lewis acidused in the instant invention is aluminum bromide. However, thefollowing Lewis acids may be used effectively: AlBr Cl, AlBrCl and BBrOther Lewis Acids such as TaF NbF,, SbF,,, AsF BCl BI} and AlCl; may beused with tetrachlorobenzene at concentrations up to their solubilitylimit. Any such Lewis acid is operable in the subject invention providedthere is no specific deleterious reaction between the Lewis acid and thesolvent employed in said reaction.

The solvent is a tetrahalosubstituted benzene. Specifically,1,2,3,4-tetrachlorobenzene, 1,2,3,4-tetrabromobenzene,1,2,3,4-tetrafluorobenzene and l,2,3,4-tetraiodobenzene may beeffectively used as a solvent for the subject reaction. Preferably, thetetrachloro, bromo and fluoro substituted benzenes are utilized. Othersol vents which produce an extremely rapid reaction rate whileminimizing side reactions are as follows: pentachlorobenzene,pentafluorobenzene and pentabromobenzene.

Ths isomerization of the instant invention will take place at atemperature between ambient and 254C. Preferably, the temperature of theisomerization ranges from ambient to 125C.

The tetrachlorobenzene to be utilized in the instant invention is asolid which melts at 475C. It forms partially miscible liquid systemswith paraffins and AlBr at room temperature and may be used between 25C.and its boiling point of 254C. as a solvent for these reactions, buttemperatures between 50C. and C. are preferred. In general, it isdesirable to isomerize at as low a temperature as possible because theequilibrium isomer distribution then contains the highest concentrationof the most branched isomers. Isomerization rate increases with suchsolvents are approximately 10 to 20 times the isomerization rate whenutilizing 1,2,4- trichlorobenzene.

The catalyst solution should be present in a volume ratio of 10/1 to0.1/l relative to the volume of feed, preferably 2:1 to 0.5:1 and mostpreferably 1:1 to 0.5: 1. In. preferred embodiments of the instantinvention, the homogeneous catalyst will convert the folowing:

n-pentane and n-hexane to the equilibrium mixture of isomers any xyleneto an equlibrium mixture of isomers cycloh exane to equilibrium withmethylcyclopentane.

A catalyst of aluminum bromide and l,2,3,4-tetrachlorobenzene isprepared by dry mixing the solid components at room temperature. Themixture melts readily near 40C. when mixed with hexane.

Pressures may vary widely but a range of one atmosphere to 100atmospheres are acceptable. The preferred range for pressure would bebetween one atmosphere and 15 atmospheres.

The Lewis acids should be present in the solvent at a relatively highconcentration which ranges from 0.1 to more than 3.0 molal solutions inthe. solvent, preferably 2.0 to 3.7 molal solutions with AlBr The acidsolution is mixed with a hydrocarbon feedstream in a ratio of 0.1 to 4volumes of hydrocarbon per 1 volume of acid, preferably in the ratio of1:1 to 2:1. In addition to the Lewis acid, there may be a minor amountof a promoter such as methyl t-amyl ether, I-I,O or HBr added to thecatalyst component. The promoter serves the function of easing theformation of carbonium ions which are the reaction intermediates. Thepromoter if utilized, is present at a concentration of 0.001 to 0.1moles/liter based on the Lewis acidsolvent mixture.

In addition, it has been discovered that a highly selectiveisomerization can be effected if hydrogen under pressures ranging frompsig to 200 psig is employed. A selective isomerization is defined forthe purposes of this invention as one in which the ratio of crackedproducts formed to 2,2-dimethylbutane in the case of the isomerizationof hexane is less than 0.1 :1. It has also been noted that the hydrogenincreases the life expectancy of the catalyst and protects it fromdeactivation. The reason for deactivation is believed to be because ofthe slow formation of unsaturated cyclic compounds which act as basestowards the acid system and thus neutralize the catalyst.

The contacting between the catalyst and the hydrocarbon feed stream maytake place in a batch or continuous operation. It is preferred to use acontinuous operation in which flow rates of about 0.1 to about 10V/V/l-lr. are utilized, preferably 0.1 to 3 and mostpreferably 0.5 to2.0 V/V/Hr.

For a batch operation, the following apparatus would be utilized; areactor made from steel or monel, preferably containing inert walls;such as glass, porcelain or Teflon, although these arenot required. Theapparatus should also be fitted with provisions for stirring, adding andwithdrawing the reactants utilized in isomerization as well as theproducts. The products are separated from the catalyst by standard meanssuch as distillation. in a continuous operation, the apparatus wouldcontain sections for the continuous introduction of feed streams to thereactor and for the continuous withdrawal of the catalyst-solventhydrocarbon system to a standard separator. Product would be collectedat the separator and the catalyst and solvent would be recycled to thereactor. Provision would be required for the continuous introduction ofsmall amounts of the catalyst and promoter to replace that which isconsumed during the operation.

Although not intending to be bound byany specific theory as tooperation, the favorable results achieved with the instant invention,i.e., minimization of side reactions and maximum rate for theisomerization are believed to stem fromthe fact that the solvents,disclosed herein generally contain aromatic rings of very low basicitybecause of the electron withdrawing properties of the halidesubstituents as has been indicated above. This property in itself is notsufficient to, control side reactions but it is a contributing factor.Thus, side reactions are controlled in this. systemv by addingconventional cracking inhibitors such as methylcyclopentane or otherwell-known naphthenes and hydrogen. These in combination with with theweakly basic solvents allow a very selective isomerization.

In a preferred embodiment of the instant invention, a feed stream whichwould be a C5 paraffin stream is isomerized over an aluminum bromidecatalyst which was contained in l,2,3,4-tetrach1orobenzene. Thehydrocarbon to be isomerized is present in an amount of one volume whilethe catalyst solution is present in the amount of 0.5 to 2 volumes andincludes a promoterv which is l-lBr at a partial pressure of '1 to 5atmospheres. The catalyst solution hasa 2.0 to 3.7 mola1 concentrationof aluminum bromide. The isomerization reaction takes place at atemperature of 65 to 100C., a pressure of 1 atmosphere to -atmospheresand on a continuous basis at a flow rate of 0.2 to 2.0Vo1.feed/Vol.Cat.Hr. The resulting product contains more than 90 percentof an essentially equilibrium mixture of hexanes and less than 10percent undesired side products which are mainly butanes and pentanes.

1n isomerizing the various hydrocarbons over the aluminum bromidecatalyst when set forth in the particular solvent that we havefound toincrease the overall activity of the catalyst, the addition of hydrogenwill prevent side reactions. In addition, when unsaturated compounds arepresent which tend to reduce the efficiency of the catalyst system, itis within the scope of this invention that we add a hydrogenationcomponent so that a hydrogenation reaction can occur. The hydrogenpressures are maintained in a range ranging from about 10 pounds to 200pounds per square inch gauge and the hydrogenation component is a GroupV111 metal such as platinum, palladium, ruthenium, rhodium, rhenium,supported on carbon, alumina, silica, or inert polymers like Teflon.

Commercially available catalysts obtained from Engelhard have beengenerally found to be acceptable hydrogenation components. Catalystscontaining about 5 percent metal on carbon have been most useful,particularly those. available in Engelhards catalyst testing kits. About5 percent of the platinum on carbon catalyst when added to the AlBr-tetrachlorobenzene system provides a strong enough hydrogenation component to convert 6 percent benzene in a C, feed to cyclohexane in 4-6hours with a hydrogen pressure of -80 psig. Platinum and palladium arethe most active Group VIII metals but a number of alloys like Pt-Rh alsoparticularly effective. The alloy containing 30% Pt 70% RhO on C isavailable from Engelhard but other alloys of Pt and other Group VIIImetals may be used.

Suitable supports for the hydrogenation catalystsinelude silica, glassbeads, glass chips and glass fibers. Inert polymers such as thosebelonging to perfluorinated series like Teflon and Kel-F are also usefulfor supporting this hydrogenation catalyst. These supports aremade'commercially and no further description of them is believednecessary.

EXAMPLE 1,

The following runs are used to illustrate the process of the instantinvention.

Uncorrected G.C. analysis From the above it is seen thatl,2,3,4-tetrachlorobenzene yields a far more active catalyst than 1,2,4-trichloro-benzene. Thus, the .overall conversion in comparative'runs 2and 3 shows about an 18 fold increase in overall activity of thel,2,3,4-tetrachlorobenzene system vs 1,2,4-trichlorobenzene underotherwise identical conditions.

EXAMPLE 2 The active catalyst in Table I did not yield a very selectiveproduct, i.e., the ratio of isomerization to cracking was only 0.25/l.However, as mentioned above, the selectivity can be markedly improved byadding a naphthene inhibitor to the feed. In Table II another comparisonis made which illustrates the ability of methylcyclopentane to controlcracking in this system.

TABLE II 2M AlBR,"-l,2,3,4

C .,H,Cl. gm 0.50 0.50 0.50 0.50 n-hexane, ml. 0.25 0.25 0.25 0.25 HBr,atm. l l l l Methylcyclopentane,

Vol. in C, O 6 24 30 Time, hr. 3 3 3 3 Temp. C. 65 65 65 65 C Isom., 3680 71 64 lsomerization/cracking 0.8/1 33/] 50/l 50/l This is a 2 molalmixture of AlBr in l,2,3,4-C.H,Cl,,

EXAMPLE 3 In Table III, it is shown that adding a naphthene to anisomerization reaction carried out in the presence of an aromaticinhibitor results in much improved isomerization, particularly withrespect to selectivity.

TABLE III 2M AlBr,-l,2,3,4C,H,Cl.,, gm 0.5 0.5 n-hexane, ml 0.25 0.25HBr, atm. 0.5 0.5 Benzene, Vol. in C 0.] Methylcyclopenatne, Vol. in C,0 6 Time, hr. 3 3 Temp. C. 95 95 C. Isom., 40 87 Isomerizationlcracking0.7/l 50/l Thus, adding 6%methylcyclopentane to a feed containing.0.l%benzene at 85C. leads again to a change in the isomerization/crackingratio from 0.7/1 to 50/ l.

EXAMPLE 4' In Table IV it is shown that the addition of percent of ahydrogenation component, (5% Pt/c) and 80 psig I-l to the AlBr -l,2,3,4-tetrachlorobenzene system permits the isomerization of n-hexanecontaining 7 percent benzene.

TABLE IV Hydrogenation of Benzene and Hexane Isomerization with DualFunction Catalyst Conditions: 95%-3M AlBr -OCl 5%-5% Pt/C; gm

Hexane Feed, 20 ml 65C., 80 psig H Product,

Mol. Pct. Feed 4 hr. 6 hr.

C, V .03 iC Tr .7 nC, .03 iC, Tr .5 nC, .03 22 DMC l9.6 44.5 23 DMC.ZMC, Tr 44.0 31.8 3 MC; Tr 16.] 10.0 nC 93.3, 92,6 l4.7 5.4 MCP Tr 1.50.5 C,,C, 4.! 6.4 C ll. 6.7. 7.4 0.0 0.0

In this experiment, benzene was hydrogenated and converted to a. mixtureof cyclohexane and methylcyclopentane. The hexane isomerization waspromoted by trace components in the system, mainly 7 percent water onthe carbon. Negligible isomerization occurred in a blank experiment withEngelhards carbon base but no platinum. Table IV therefore shows a rapidand selective isomerization of n-hexane containing benzene over the dualfunction catalyst.

The beneficial effect of hydrogen in the absence of any specialhydrogenating component is demonstrated in this example. Two continuousisomerization runs are shown, each with the same C feed, feed rate,catalyst and temperature.

Partial Partial Pressure Pressure Run Psig Psig HBr Psig H, Life hr. A30 30 0 5-10 B 60 6-l 2 48-S4 200 In Run A only HBr was added to thefeed. It served the dual function of providing the catalyst initiatorand being the stripping gas required to keep a constant amount ofhydrocarbon in the reactor. At 30 psig HBr, rapid isomerization wasinduced but the catalyst life was shortlived as shown by a rapidconversion to 40 percent 2-2-dimethylbutane and a subsequent rapid dccline in activity. The useful life of the catalyst was about 5 to 10hours.

In Run B, I-IBr and H, are used together. The HBr partial pressure wasvaried through the run but generally, was 6-12 psi while the H, partialpressure was about 50 psi. The useful life was extended to over 200hours for this system showing more than an order of magnitudeimprovement in catalyst life when H, is used with HBr.

What is claimed is:

1. A process for isomerizing hydrocarbons which comprises contactingsaid hydrocarbons under isomerization conditions in the liquid phasewith a Lewis acid catalyst, said contacting taking place within asolvent, said solvent being a benzene in which at least four of thecarbons have a substituent selected from the group consisting ofchlorine, bromine, fluorine and iodine.

2. The process of claim 1 in which the solvent is selected from thegroup consisting of l,2,3,4-tetrachlorobenzene andl,2',3,S-tetrachlorobenzene, pentachlorobenzene and pentafluorobenzene.

3. The process of claim 1 wherein said hydrocarbon is a C -C paraffin.

4.The process of claim 1 wherein said hydrocarbon is aromatic.

5. The process of claim 1 wherein said catalyst contains a minor amountof a promoter.

'6. The process of claim 1 wherein said hydrocarbon is a xylene.

7. The process of claim 1 wherein a naphthene is added to the catalyst.

S. The process of claim 7 wherein said naphthene is methylcyclopentane.

9. The process of claim 1 wherein said catalyst is aluminum bromide.

10. The process of claim 1 further including the step of adding hydrogenunder mild conditions to the liquid phase.

11. The process of claim 10 wherein said contacting is carried out inthe presence of a hydrogenation component.

12. The process of claim 11 wherein said hydrogenation component isplatinum deposited on carbon.

13. The process of claim 12 wherein the carbon contains 0.1 to 10percent weight of platinum.

14. A process for isomerizing C to C paraffins which comprisescontacting said paraffins in the liquid phase with an aluminum bromidecatalyst, said contacting taking place within a solvent comprisingl,2,3,4-tetrachlorobenzene and recovering an isomerized paraffin.

15. The process of claim 14 wherein said contacting takes place at atemperature of 25 to l50C.

16. The process of claim 14 wherein said contacting takes place in thepresence of hydrogen.

17. The process of claim 16 wherein said contacting takes place in thepresence of a hydrogenation catalyst.

18. The process of claim 17 wherein the hydrogenation component iseither a Group VIII metal or an alloy of Pt with one or more Group VIIImetals supported on carbon.

19. The process of claim 18 wherein the support may be one selected fromthe group consisting of silica,

glass beads, glass chips, glass fibers and inert polymers.

* i ii i

2. The process of claim 1 in which the solvent is selected from thegroup consisting of 1,2,3,4-tetrachlorobenzene and1,2,3,5-tetrachlorobenzene, pentachlorobenzene and pentafluorobenzene.3. The process of claim 1 wherein said hydrocarbon is a C4-C7 paraffin.4. The process of claim 1 wherein said hydrocarbon is aromatic.
 5. Theprocess of claim 1 wherein said catalyst contains a minor amount of apromoter.
 6. The process of claim 1 wherein said hydrocarbon is axylene.
 7. The process of claim 1 wherein a naphthene is added to thecatalyst.
 8. The process of claim 7 wherein said naphthene ismethylcyclopentane.
 9. The process of claim 1 wherein said catalyst isaluminum bromide.
 10. The process of claim 1 further including the stepof adding hydrogen under mild conditions to the liquid phase.
 11. Theprocess of claim 10 wherein said contacting is carried out in thepresence of a hydrogenation component.
 12. The process of claim 11wherein said hydrogenation component is platinum deposited on carbon.13. The process of claim 12 wherein the carbon contains 0.1 to 10percent weight of platinum.
 14. A process for isomerizing C4 to C6paraffins which comprises contacting said paraffins in the liquid phasewith an aluminum bromide catalyst, said contacting taking place within asolvent comprising 1,2,3,4-tetrachlorobenzene and recovering anisomerized paraffin.
 15. The process of claim 14 wherein said contactingtakes place at a temperature of 25* to 150*C.
 16. The process of claim14 wherein said contacting takes place in the presence of hydrogen. 17.The process of claim 16 wherein said contacting takes place in thepresence of a hydrogenation catalyst.
 18. The process of claim 17wherein the hydrogenation component is either a Group VIII metal or analloy of Pt with one or more Group VIII metals supported on carbon. 19.The process of claim 18 wherein the support may be one selected from thegroup consisting of silica, glass beads, glass chips, glass fibers andinert polymers.